The present invention relates to an electronic timepiece motor which comprises a permanent magnet rotor and a stator made of magnetic members, and more particularly to the stator structure which includes a non-magnetic reinforcing member.
A stator for use in an electronic timepiece motor is generally made in pairs (two pieces), and each of the stator pieces have semi-cylindrical surfaces which are opposite a rotor. There are, however, several disadvantages associated with the conventional stator. Namely, two piece stators result in a double cost since raw materials of the stator are magnetic material such as permalloy, pure iron, silicon-steel plate or the like which are exceedingly expensive in themselves, and which are poor in workability and the processing costs of punching, annealing or the like are very high. Moreover, since a pair of opposing stators should be positioned accurately upon completion of the assembling process, adjustable positioning structure which enables the position adjustment of the stator pieces after assembling is required.
To eliminate the adjusting process, a one-piece stator is first mounted on a stainless steel plate by means of a pin, caulking, welding or the like and then only the stator portion is cut to separate the one-piece stator into two pieces. However, this technique is troublesome and cannot solve the cost problem.
On the other hand, in order to eliminate the above mentioned problems, a one-piece stator is used. The form of one-piece stator is like a pair of conventional opposed stator pieces coupled together. The sectional area of a coupling portion is greatly reduced in order to generate a leak-off magnetic field at the surrounding portion of the rotor due to saturation caused by enhancement of magnetic resistance. The rotation efficiency is excessively diminished under the influence of the above mentioned leak-off magnetic field if the sectional area is too large and it may not be used in a timepiece which necessitates accuracy. Moreover, since the sectional area is exceedingly small, it is apt to be formed during the process of timepiece assembly or the like, and therefore the rotation efficiency may be degraded due to the deformation of the sectional area. Thus, the one-piece stator has drawbacks which prevent its practical use.